This is a competitive renewal of a contract that is now in its third year at the University of Maryland. This award for an additional three years has as its objective the continued development and further refinement of an existing quantitative model of the structure and function of the cat hindlimb and its musculoskeletal components. Specifically, the existing model will be extended to include a description of motion in the toe segments, descriptions of the internal architecture of each of the 33 muscles, development of a mathematical relationship among excitation measurements (EMG) and the kinematic terms of velocity and length of the muscle sarcomeres, and "userfriendly" interfaces by which experimentalists can introduce and manipulate experimental data and receive graphical output of model projections.